Linux 内核模块链接器警告：“*** 警告：” [<模块>] 未定义！” - 有什么方法可以摆脱它们吗？

发布于 2024-07-14 22:04:45 字数 424 浏览 4 评论 0原文

在编译相互依赖的 Linux 内核模块时，链接器会给出未定义的符号警告，例如

 Building modules, stage 2.
 MODPOST
*** Warning: "function_name1" [module_name] undefined!
*** Warning: "function_name2" [module_name] undefined!
*** Warning: "function_name3" [module_name] undefined!

使用 insmod 或 modprobe 将模块插入内核后，未解析的符号将立即解析。有什么办法可以消除链接器警告吗？

我已经阅读了 3 个关于这个问题的 Google SERP - 似乎没有人知道答案。当您构建内核模块时，这些链接器警告应该是这样的吗？

原文

While compiling Linux kernel modules that depend on each other, linker gives undefined symbol warnings like

 Building modules, stage 2.
 MODPOST
*** Warning: "function_name1" [module_name] undefined!
*** Warning: "function_name2" [module_name] undefined!
*** Warning: "function_name3" [module_name] undefined!

The unresolved symbols are resolved as soon as module is inserted into kernel using insmod or modprobe. Is there any way to get rid of the linker warning, though?

I have read through 3 Google SERP's on this issue - it seems nobody knows the answer. Are these linker warnings supposed to be this way when you build a kernel module?

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傲鸠 2024-07-21 22:04:45

使用 KBUILD_EXTRA_SYMBOLS 如下：
KBUILD_EXTRA_SYMBOLS='你的模块路径'/Module.symvers

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极致的悲 2024-07-21 22:04:45

最后我得到了它。感谢 Shodanex 让我走上了正确的道路。

更新：将此修复应用于旧版本内核的构建时要非常小心，因为旧版本的 Makefile.modpost 文件中存在错误当您指定 KBUILD_EXTMOD 选项时，内核版本会导致您的构建行为不当并构建错误的目标。

您必须在 KBUILD_EXTMOD make 参数中指定您所依赖的模块的源路径。

假设您有一个模块 foo，它依赖于模块 bar 中的符号。

foo 的源文件位于 foo/module/ 中，bar 的源文件位于 bar/module/ 中

Makefile 中的 make 命令 for foo 可能看起来像

make ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE -C $LINUX_DIR \
    M=`pwd`/module \
    modules

（确切的行可能在您的项目中有所不同）。

将其更改为

make ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE -C $LINUX_DIR \
    M=`pwd`/module \
    KBUILD_EXTMOD=`pwd`/../bar/module \
    modules

（我们添加了 KBUILD_EXTMOD=pwd/../bar/module \ 行，其中 pwd/../bar/module 是内核源代码的路径我们所依赖的模块。

人们期望 KBUILD_EXTRA_SYMBOLS 参数以这种方式工作，但它是 KBUILD_EXTMOD。

Finally, I got it. Thanks to shodanex for putting me on the right track.

Update: Be very careful when applying this fix to builds for older versions of kernel, as there is a bug in Makefile.modpost file in older versions of the kernel which makes your build misbehave and build wrong targets when you specify KBUILD_EXTMOD option.

You have to specify the paths to the source of the modules you depend on in KBUILD_EXTMOD make parameter.

Say, you have a module foo that depends on symbols from module bar.

Source files for foo are in foo/module/ and source files for bar are in bar/module/

The make command in Makefile for foo probably looks like

make ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE -C $LINUX_DIR \
    M=`pwd`/module \
    modules

(the exact line may differ in your project).

Change it to

make ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE -C $LINUX_DIR \
    M=`pwd`/module \
    KBUILD_EXTMOD=`pwd`/../bar/module \
    modules

(we added the KBUILD_EXTMOD=pwd/../bar/module \ line, where pwd/../bar/module is a path to sources of kernel module we depend on.

One would expect KBUILD_EXTRA_SYMBOLS parameter to work this way, however it's KBUILD_EXTMOD.

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つ低調成傷 2024-07-21 22:04:45

不，他们不是。无论您在树内还是树外构建代码，都不应显示此消息。我认为您应该修复您的 Makefile。这是一个 makefile 示例。不完美，但曾经可以工作（直到 2.6.26，此后就没有尝试过）：

ifneq ($(KERNELRELEASE),)
# We were called by kbuild

obj-m += mymodule.o 
mymodule-objs := mymodule_usb.o a.o b.o c.o

else  # We were called from command line

KDIR := /lib/modules/$(shell uname -r)/build
PWD  := $(shell pwd)

default:
    @echo '    Building FOO drivers for 2.6 kernel.'
    @echo '    PLEASE IGNORE THE "Overriding SUBDIRS" WARNING'
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

install:
    ./do_install.sh *.ko

endif  # End kbuild check

clean:
    rm -f -r *.o *.ko .*cmd .tmp* core *.i

有关进一步的文档，您可以检查内核树，kbuild 过程是记录

No they are not. Wheter you build your code in-tree or out of tree, this message should not be displayed.I think you should fix your Makefile. Here is an example makefile. Not perfect, but used to work (until 2.6.26, did not try it since) :

ifneq ($(KERNELRELEASE),)
# We were called by kbuild

obj-m += mymodule.o 
mymodule-objs := mymodule_usb.o a.o b.o c.o

else  # We were called from command line

KDIR := /lib/modules/$(shell uname -r)/build
PWD  := $(shell pwd)

default:
    @echo '    Building FOO drivers for 2.6 kernel.'
    @echo '    PLEASE IGNORE THE "Overriding SUBDIRS" WARNING'
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

install:
    ./do_install.sh *.ko

endif  # End kbuild check

clean:
    rm -f -r *.o *.ko .*cmd .tmp* core *.i

For further documentation, you can check the kernel tree, the kbuild process is documented

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